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While researching Antarctic geology, I came across the term 'icequake' in the abstract to the article Seismicity within a propagating ice shelf rift: The relationship between icequake locations and ice shelf structure (Heeszel et al. 2014).

These events are also known as cryoseisms - in reference to glaciers, the Wikipedia article describes a cryoseism as:

a non-tectonic seismic event caused by sudden glacial movements. This movement has been attributed to a veneer of water which may pool underneath a glacier sourced from surface ice melt. Hydraulic pressure of the liquid can act as a lubricant, allowing the glacier to suddenly shift position. This type of cryoseism can be very brief, or may last for several minutes.

and describe them as being able to

have an intensity of up to VI on the Modified Mercalli Scale

Is there a limit to how high glacial icequake magnitudes (Richter Scale) can be?

Azzie Rogers
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    This link records an icequake of 3,8 Richter - but that wasn't the strongest one in the world, just in the Madison's lakes region. I would expect the strongest ones to occur in Antarctica and avoid measurement. – Pavel V. Aug 11 '15 at 17:59

2 Answers2

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One way to estimate the upper limit of the magnitude is through observations and measurements. According to the article Seismic Wave Interactions Between the Atmosphere - Ocean - Cryosphere System and the Geosphere in Polar Regions, a couple of difficulties with determining how large ice-quakes can get, asides from the regions not monitored, are due to the sources of the recorded motion and delineating cryoseismic and tectonic observations. From the article:

Such cryoseismic sources include the movements of ice sheets, sea-ice, oceanic tide-cracks, oceanic gravity waves, icebergs and the calving fronts of ice caps. At times, it can be hard to distinguish between the waveforms generated by local tectonic earthquakes and those of ice-related phenomena.

However, in the Scientific American article Long-Overlooked "Ice Quakes" Data Provides Insights into Calving Glaciers, they can be identified by their location and unique waveforms identified relatively recently.

According to the first article, unlike tectonic events, cryoseismic (= ice-quake) events are seasonal and heavily climate-dependent, with the article detailing that observations have shown that in polar regions

microseism amplitude is attenuated during local winter for both primary and secondary microseisms

Observations of body-wave magnitudes (Mb) between 1987-2007 in an Antarctic station were up to 6.5-7.0

A recent observation are the related 'glacial quakes', which generated log period surface waves (greater than 25s) which, according to the article, is

equivalent in strength to those radiated by standard magnitude five earthquakes, and were observable worldwide. The glacial earthquakes radiated little high-frequency energy, which explains why they were not detected or located by traditional earthquake-monitoring systems. These events are two magnitude units larger than previously reported seismic phenomena associated with glaciers, a size difference corresponding to a factor of 1,000 in a seismic moment.

Similar observations have been made in the Greenland ice sheet.

NOAA has some sample cryoseismic traces on their PMEL Acoustics page Icequakes.

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This isnt an answer, but may point you in the right direction

http://eost.u-strasbg.fr/semipgs/pres_Walter_04_03_08.pdf

Patrick Meddaugh
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    Could you provide a summary of the relevant points in the document in addition to the link? – arkaia Aug 11 '15 at 01:29
  • @aretxabaleta I could sure, but it would be a rough summary at best as it does contain a lot of equations and its a bit out of my realm of expertise. If it would be helpful I can take a stab though. – Patrick Meddaugh Aug 14 '15 at 20:07